A voice coil motor linear actuator uses a coil disposed around a magnet to generate a linear motion. Linear actuators are commonly used in tape drives to move a tape head used to read and/or write to a tape. The tape head is attached to a supporting structure. The linear actuator moves the supporting structure, causing the head to move across the tape. Recording head actuators require high bandwidth linear head motion: the head position changes to keep the head in the correct location on the media must be made quickly. One method to increase the speed by which the head is positioned relative to the media is to increase the force used to drive the head.
In a voice coil motor linear actuator, current is transmitted through the coil, generating a linear force to actuate the head. Typically, the coil is actuated while the magnet is stationary. U.S. Pat. No. 8,422,173 B2 (“the '173 patent,” incorporated herein by reference in its entirety) discloses a dual pole magnet linear actuator that includes a stationary coil disposed around an actuated magnet. It is advantageous to actuate the magnet instead of the coil, as actuating the magnet significantly reduces vibrational resonances interfering with the head, as compared to actuating the coil.
In a voice coil motor, the coil may be wrapped around one side of the magnet, and the coil is actuated up and down about one pole of the magnet. Traditional voice coil motors only take advantage of the magnetic flux on one end of the magnet. The '173 patent discloses a dual pole magnet linear actuator that extends the coil about both poles of the magnet, increasing the region in which the motor generates linear force.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.